Fixture for magnetizing toroidal permanent magnets



F. x. MHGDONOUGH ETAL 2,897,417

FIXTURE FOR MAGNETIZING TOROIDAL PERMANENT MAGNETS Filed Oct. 17, 1957 2Sheets-Sheet 1 H41 j" 3 FIG. 1

INVENTOR. PEAK/5' A. MKDO/VOUGI/ LESL/E M VAN? ATTOENE)? July 28, 1959F. x. M DONOUGH El AL 2,897,417

FIXTURE FOR MAGNETIZING TOROIDAL PERMANENT MAGNETS Filed Oct. 17, 1957 2Sheets-Sheet 2 oha z" A TOE/V5) United States Patent FIXTURE FORMAGNETIZING TOROIDAL PERMANENT MAGNETS Francis X. MacDonough, Stoneham,and Leslie M. Vant, Reading, Mass., assign'ors to Bomac LaboratoriesInc., Beverly, Mass., a corporation of Massachusetts Application October17, 1957, Serial No. 690,767

2 Claims. (Cl. 317-203) The present invention relates to electrondischarge devices of the type having toroidal or bowl-shaped permanentmagnets and more particularly to a novel method of and fixture formagnetizing such magnets,

Electron discharge devices in which permanent magnets are employed toproduce the transverse magnetic field necessary for the flow ofelectrons include magnetron and backward wave oscillators. A developmentof recent origin discloses a toroidal magnet completely enveloping thetube for maximum efiiciency and elimination of the side and outsideleakage flux components. A detailed description will be found in U.S.Patent No. 2,787,728, issued April 2, 1957, to P. W. Crapuchettes.

The primary object of the present invention is the provision of a novelmethod of and fixture for magnetizing toroidal permanent magnets.

Another object is the provision of a magnetizing method and fixture fortoroidal magnets which achieves magnetic saturation efiieiently andrequires a less costly operation.

The common method of magnetizing magnets heretofore employed involve theuse of either a single internal loop or multi-turn external coilstogether with an elaborate impulse circuit under the so-called bruteforce method.

The main disadvantage in the use of the single loop resides in the factthat the magnetizing must be performed prior to assembly of the magnetsto the tube body. Problems of retaining the field while assembling themagnets, preventing attraction of metallic particles in the area of themating surfaces or possible tube damage will arise with this method.Further, space limitations between the magnets and the tube bodygenerally preclude the use of this method.

The alternative method employing multi-turn coils of a low currentcapacity wire on the outside of the magnet does not achieve satisfactorysaturation or stability when employed for toroid shaped magnets,

In accordance with the teachings of the present invention there isprovided a novel method and fixture for magnetizing the paired toroidalmagnets mounted on a completed tube body assembly. Broadly, theinvention provides a fixture having a configuration which completelysurrounds the magnet. The fixture may be cast from a highly conductivematerial such as copper and is designed to handle [high peak currents inthe order of 200,000 amperes. A gap is provided along the radius of thecast member to interrupt the conductive path and essentially form anexternal single loop of relatively large mass. A connector may be castin the fixture to mate with a similarly fabricated member. The matingfixtures are then connected to an impulse type magnetizer capable ofgenerating extremely high current pulses of short duration. With thefixture and method disclosed herein saturation and stability will berealized in magnetizing toroidal magnets.

The aforementioned features, objects and advantages will be apparentafter consideration of the following detailed description of a selectedembodiment and reference to the accompanying drawings, in which:

Fig. l is a view partly in section of the embodiment of the invention inthe operative position with an electron discharge device having toroidalmagnets shown in perspective;

Fig. 2 is a perspective view of the embodiment shown with an oppositelydisposed similar embodiment, to illustrate the method of the invention;and

Fig. 3 is a view of the magnetic return path keeper assembly employedwith the embodiment of the invention.

Referring now to Figs. 1 and 2 the illustrative device 1 employingtoroidal magnets is a magnetron of conventional construction. Onlyexternal structure has been shown since this is material to adescription of the invention. The tube envelope is completely surroundedby the toroidal magnets 2 and 3 and has two axial extensions enclosingthe ends of the envelope. Extension 4 encloses the cathode supportassembly with terminals 5, 6 and 7. Extension 8 houses the tuningassembly with the actuator assembly omitted for simplicity. Threaded rod9 forms the connecting means for the actuator.

According to the teachings of the invention, the magnetizing fixture 10comprises a substantially frusto-conical shaped member 11 having atapered axial passageway 12 for accommodation of the tube extensionspreviously described. Member 11 is fabricated in the form of a castingof a highly conductive metal such as for example copper. An enlargedconnector tab 13 having an aperture may also be cast as an integral partof member 11 along the periphery of the widest dimension.

The inside of member 11 is hollowed to define a receiving chamber 15conforming to the overall shape of the toroidal magnet 2 or 3. Hence theoverall fixture resembles a bowl or skull cap. Notches 16 and 17 arealso provided to allow for other external magnetron structure not shown,such as the output coupler which is positioned within notch 16. An airgap formed by a saw cut 18 along the radius of member 11 as well asanother saw cut 19 along the joining edge of the tab 13 converts thefixture into effectively a single open-ended loop. A conductor cable 20may be secured to the member 11 as shown at 21 with a copper block 23 atthe outer end for connection to the magnetizing circuit. A 600 amperewelding cable may for example be selected.

The method of the invention will now be described employing a pair ofsimilar bowl fixture members 10 in oppositely disposed relationship. Thetube 1 with assembled magnets 2 and 3 may, therefore, be completelyenveloped by the fixture members and is retained in this position bymeans of a steel bolt and nut arrangement 24. To assure good contactbetween the mating surfaces of tabs 13 and to act as a separator of themating surfaces of members 10 a strip of copper wire mesh 14 may beutilized. Steel pole pieces 25 and 26 are then inserted in passageways12 and encircle tube extensions 4 and 8 respectively to concentrate theflux developed by fixture members 10 into the lowest reluctance pathalong the axis of symmetry of the tube. Conductors 20 may then befastened to appropriate leads from an impulse magnetizer having a verylow impedance. As an example, a Model 8100 Raytheon Manufacturing Co.condenser discharging type impulse magnetizer provides for currentpulses up to 200,000 amperes peak with a DC charging voltage adjustableto 3000 volts. With this equipment and the magnetizing fixture of theinvention saturation may be achieved in a matter of milliseconds.

In the design of the embodiment of the invention consideration wasdirected to the concentration of magnetic flux along the axis ofsymmetry of the device where the tube electrode structure requiring anintense magnetic 3 t field is located. Hence in the bowl-shaped fixturethe cross sectional area adjacent the passageway 12 as indicated by theline AA was increased to approximanl tw e he ants. e ti na a a f the Wal t ut: we defining cham 15 a ndica d b th l n .+B b low t l e c a Fi 1Wit t i n rati greater conductivity exists around the reducing neclipor- @9 @1 6 n e the P rt n ar n a ama cu rent will How in the neckregion. Efife'ctively more, ampere turns are produced in this regionwhich leads to an' inreat d ma n iz n force According to k o et z n P oedure m tal i e r m b P o e t Su p y the ma n tic ater thereby a r n a ua io wi h a minim m o fii h r e o bow current n am le o one y t j pl y dhown, in 3 comp s n s l shorting has 27 a d Z i i m y b s cu ed to nsepole Pieces 2.5%?? with hr d d ro 2 a d 3 te d n therebs w Re a n nut 3swr d 9 th n o d 2 9 and 3,0 retain the overall fixture assembly.

It may also be advisable to insulate the mating surfaces of members 10in the region adjacent the connecttabs 13. Hence the rim 32 on the sideof the loop secured to conductors 20 may be coated with any satisfactory insulating material, for example, paint or tape. This willprevent accidental by-passing or shunting of current between theconductor cables 20. It is necessary that all the current must flowthrough each bowl in the tend d P t With the method and fixturedisclosed herein the toroidal magnet may be demagnetized simply by thereversal of the current flow or reversal of the tube within the bowlfixture,

What is claimed is:

1. A fixture for use in the impulse method of magnetizing pairedtoroidal magnets oppositely disposed on a magnetron tube having tubularextensions, said fixture comprising a pair of similar frusto-conicalshaped metallic members adapted to completely envelop the magnetronmagnets when said members are in mating relah n th ar e en s, in cqn q ech o said metallic members having wall structure commencing at the, L eend de n g q o tti t d m ns tntd 1Q t0. the afiaurati i of c ma et, a conectortab. laterally disposed at a point along the peripheral edgeadjacent' the large end, said member being bisected throughout itslength by means of a slot commencing adjacent to said tab to therebydefine an open ended loop of large mass and current conducting meanssecured to said member along the outer surface thereof for connection toan impulse magnetizing apparatus.

K fiigtureaccording to claim' 1 wherein the ratio of the cross sectionalarea of the wall structure at the conical end to the cross sectionalarea of the wall structure of the hollow portion surrounding the magnetis approximately 2:1 P

References Cited in the file of this patent UNITED, .STATES PAT NTSOTHER REFERENCES is m u a cti e for e a en Magne s:

Electronics, August l95 5, pages 12 112 3.

